Initexternals/with-command-redo

8 files changed, 1489 insertions, 0 deletions

diff --git a/.elisp-autofmt b/.elisp-autofmt
new file mode 100644
index 0000000..e69de29
--- /dev/null
+++ b/.elisp-autofmt
diff --git a/LICENSE b/LICENSE
new file mode 100644
index 0000000..f288702
--- /dev/null
+++ b/LICENSE
@@ -0,0 +1,674 @@
+                    GNU GENERAL PUBLIC LICENSE
+                       Version 3, 29 June 2007
+
+ Copyright (C) 2007 Free Software Foundation, Inc. <https://fsf.org/>
+ Everyone is permitted to copy and distribute verbatim copies
+ of this license document, but changing it is not allowed.
+
+                            Preamble
+
+  The GNU General Public License is a free, copyleft license for
+software and other kinds of works.
+
+  The licenses for most software and other practical works are designed
+to take away your freedom to share and change the works.  By contrast,
+the GNU General Public License is intended to guarantee your freedom to
+share and change all versions of a program--to make sure it remains free
+software for all its users.  We, the Free Software Foundation, use the
+GNU General Public License for most of our software; it applies also to
+any other work released this way by its authors.  You can apply it to
+your programs, too.
+
+  When we speak of free software, we are referring to freedom, not
+price.  Our General Public Licenses are designed to make sure that you
+have the freedom to distribute copies of free software (and charge for
+them if you wish), that you receive source code or can get it if you
+want it, that you can change the software or use pieces of it in new
+free programs, and that you know you can do these things.
+
+  To protect your rights, we need to prevent others from denying you
+these rights or asking you to surrender the rights.  Therefore, you have
+certain responsibilities if you distribute copies of the software, or if
+you modify it: responsibilities to respect the freedom of others.
+
+  For example, if you distribute copies of such a program, whether
+gratis or for a fee, you must pass on to the recipients the same
+freedoms that you received.  You must make sure that they, too, receive
+or can get the source code.  And you must show them these terms so they
+know their rights.
+
+  Developers that use the GNU GPL protect your rights with two steps:
+(1) assert copyright on the software, and (2) offer you this License
+giving you legal permission to copy, distribute and/or modify it.
+
+  For the developers' and authors' protection, the GPL clearly explains
+that there is no warranty for this free software.  For both users' and
+authors' sake, the GPL requires that modified versions be marked as
+changed, so that their problems will not be attributed erroneously to
+authors of previous versions.
+
+  Some devices are designed to deny users access to install or run
+modified versions of the software inside them, although the manufacturer
+can do so.  This is fundamentally incompatible with the aim of
+protecting users' freedom to change the software.  The systematic
+pattern of such abuse occurs in the area of products for individuals to
+use, which is precisely where it is most unacceptable.  Therefore, we
+have designed this version of the GPL to prohibit the practice for those
+products.  If such problems arise substantially in other domains, we
+stand ready to extend this provision to those domains in future versions
+of the GPL, as needed to protect the freedom of users.
+
+  Finally, every program is threatened constantly by software patents.
+States should not allow patents to restrict development and use of
+software on general-purpose computers, but in those that do, we wish to
+avoid the special danger that patents applied to a free program could
+make it effectively proprietary.  To prevent this, the GPL assures that
+patents cannot be used to render the program non-free.
+
+  The precise terms and conditions for copying, distribution and
+modification follow.
+
+                       TERMS AND CONDITIONS
+
+  0. Definitions.
+
+  "This License" refers to version 3 of the GNU General Public License.
+
+  "Copyright" also means copyright-like laws that apply to other kinds of
+works, such as semiconductor masks.
+
+  "The Program" refers to any copyrightable work licensed under this
+License.  Each licensee is addressed as "you".  "Licensees" and
+"recipients" may be individuals or organizations.
+
+  To "modify" a work means to copy from or adapt all or part of the work
+in a fashion requiring copyright permission, other than the making of an
+exact copy.  The resulting work is called a "modified version" of the
+earlier work or a work "based on" the earlier work.
+
+  A "covered work" means either the unmodified Program or a work based
+on the Program.
+
+  To "propagate" a work means to do anything with it that, without
+permission, would make you directly or secondarily liable for
+infringement under applicable copyright law, except executing it on a
+computer or modifying a private copy.  Propagation includes copying,
+distribution (with or without modification), making available to the
+public, and in some countries other activities as well.
+
+  To "convey" a work means any kind of propagation that enables other
+parties to make or receive copies.  Mere interaction with a user through
+a computer network, with no transfer of a copy, is not conveying.
+
+  An interactive user interface displays "Appropriate Legal Notices"
+to the extent that it includes a convenient and prominently visible
+feature that (1) displays an appropriate copyright notice, and (2)
+tells the user that there is no warranty for the work (except to the
+extent that warranties are provided), that licensees may convey the
+work under this License, and how to view a copy of this License.  If
+the interface presents a list of user commands or options, such as a
+menu, a prominent item in the list meets this criterion.
+
+  1. Source Code.
+
+  The "source code" for a work means the preferred form of the work
+for making modifications to it.  "Object code" means any non-source
+form of a work.
+
+  A "Standard Interface" means an interface that either is an official
+standard defined by a recognized standards body, or, in the case of
+interfaces specified for a particular programming language, one that
+is widely used among developers working in that language.
+
+  The "System Libraries" of an executable work include anything, other
+than the work as a whole, that (a) is included in the normal form of
+packaging a Major Component, but which is not part of that Major
+Component, and (b) serves only to enable use of the work with that
+Major Component, or to implement a Standard Interface for which an
+implementation is available to the public in source code form.  A
+"Major Component", in this context, means a major essential component
+(kernel, window system, and so on) of the specific operating system
+(if any) on which the executable work runs, or a compiler used to
+produce the work, or an object code interpreter used to run it.
+
+  The "Corresponding Source" for a work in object code form means all
+the source code needed to generate, install, and (for an executable
+work) run the object code and to modify the work, including scripts to
+control those activities.  However, it does not include the work's
+System Libraries, or general-purpose tools or generally available free
+programs which are used unmodified in performing those activities but
+which are not part of the work.  For example, Corresponding Source
+includes interface definition files associated with source files for
+the work, and the source code for shared libraries and dynamically
+linked subprograms that the work is specifically designed to require,
+such as by intimate data communication or control flow between those
+subprograms and other parts of the work.
+
+  The Corresponding Source need not include anything that users
+can regenerate automatically from other parts of the Corresponding
+Source.
+
+  The Corresponding Source for a work in source code form is that
+same work.
+
+  2. Basic Permissions.
+
+  All rights granted under this License are granted for the term of
+copyright on the Program, and are irrevocable provided the stated
+conditions are met.  This License explicitly affirms your unlimited
+permission to run the unmodified Program.  The output from running a
+covered work is covered by this License only if the output, given its
+content, constitutes a covered work.  This License acknowledges your
+rights of fair use or other equivalent, as provided by copyright law.
+
+  You may make, run and propagate covered works that you do not
+convey, without conditions so long as your license otherwise remains
+in force.  You may convey covered works to others for the sole purpose
+of having them make modifications exclusively for you, or provide you
+with facilities for running those works, provided that you comply with
+the terms of this License in conveying all material for which you do
+not control copyright.  Those thus making or running the covered works
+for you must do so exclusively on your behalf, under your direction
+and control, on terms that prohibit them from making any copies of
+your copyrighted material outside their relationship with you.
+
+  Conveying under any other circumstances is permitted solely under
+the conditions stated below.  Sublicensing is not allowed; section 10
+makes it unnecessary.
+
+  3. Protecting Users' Legal Rights From Anti-Circumvention Law.
+
+  No covered work shall be deemed part of an effective technological
+measure under any applicable law fulfilling obligations under article
+11 of the WIPO copyright treaty adopted on 20 December 1996, or
+similar laws prohibiting or restricting circumvention of such
+measures.
+
+  When you convey a covered work, you waive any legal power to forbid
+circumvention of technological measures to the extent such circumvention
+is effected by exercising rights under this License with respect to
+the covered work, and you disclaim any intention to limit operation or
+modification of the work as a means of enforcing, against the work's
+users, your or third parties' legal rights to forbid circumvention of
+technological measures.
+
+  4. Conveying Verbatim Copies.
+
+  You may convey verbatim copies of the Program's source code as you
+receive it, in any medium, provided that you conspicuously and
+appropriately publish on each copy an appropriate copyright notice;
+keep intact all notices stating that this License and any
+non-permissive terms added in accord with section 7 apply to the code;
+keep intact all notices of the absence of any warranty; and give all
+recipients a copy of this License along with the Program.
+
+  You may charge any price or no price for each copy that you convey,
+and you may offer support or warranty protection for a fee.
+
+  5. Conveying Modified Source Versions.
+
+  You may convey a work based on the Program, or the modifications to
+produce it from the Program, in the form of source code under the
+terms of section 4, provided that you also meet all of these conditions:
+
+    a) The work must carry prominent notices stating that you modified
+    it, and giving a relevant date.
+
+    b) The work must carry prominent notices stating that it is
+    released under this License and any conditions added under section
+    7.  This requirement modifies the requirement in section 4 to
+    "keep intact all notices".
+
+    c) You must license the entire work, as a whole, under this
+    License to anyone who comes into possession of a copy.  This
+    License will therefore apply, along with any applicable section 7
+    additional terms, to the whole of the work, and all its parts,
+    regardless of how they are packaged.  This License gives no
+    permission to license the work in any other way, but it does not
+    invalidate such permission if you have separately received it.
+
+    d) If the work has interactive user interfaces, each must display
+    Appropriate Legal Notices; however, if the Program has interactive
+    interfaces that do not display Appropriate Legal Notices, your
+    work need not make them do so.
+
+  A compilation of a covered work with other separate and independent
+works, which are not by their nature extensions of the covered work,
+and which are not combined with it such as to form a larger program,
+in or on a volume of a storage or distribution medium, is called an
+"aggregate" if the compilation and its resulting copyright are not
+used to limit the access or legal rights of the compilation's users
+beyond what the individual works permit.  Inclusion of a covered work
+in an aggregate does not cause this License to apply to the other
+parts of the aggregate.
+
+  6. Conveying Non-Source Forms.
+
+  You may convey a covered work in object code form under the terms
+of sections 4 and 5, provided that you also convey the
+machine-readable Corresponding Source under the terms of this License,
+in one of these ways:
+
+    a) Convey the object code in, or embodied in, a physical product
+    (including a physical distribution medium), accompanied by the
+    Corresponding Source fixed on a durable physical medium
+    customarily used for software interchange.
+
+    b) Convey the object code in, or embodied in, a physical product
+    (including a physical distribution medium), accompanied by a
+    written offer, valid for at least three years and valid for as
+    long as you offer spare parts or customer support for that product
+    model, to give anyone who possesses the object code either (1) a
+    copy of the Corresponding Source for all the software in the
+    product that is covered by this License, on a durable physical
+    medium customarily used for software interchange, for a price no
+    more than your reasonable cost of physically performing this
+    conveying of source, or (2) access to copy the
+    Corresponding Source from a network server at no charge.
+
+    c) Convey individual copies of the object code with a copy of the
+    written offer to provide the Corresponding Source.  This
+    alternative is allowed only occasionally and noncommercially, and
+    only if you received the object code with such an offer, in accord
+    with subsection 6b.
+
+    d) Convey the object code by offering access from a designated
+    place (gratis or for a charge), and offer equivalent access to the
+    Corresponding Source in the same way through the same place at no
+    further charge.  You need not require recipients to copy the
+    Corresponding Source along with the object code.  If the place to
+    copy the object code is a network server, the Corresponding Source
+    may be on a different server (operated by you or a third party)
+    that supports equivalent copying facilities, provided you maintain
+    clear directions next to the object code saying where to find the
+    Corresponding Source.  Regardless of what server hosts the
+    Corresponding Source, you remain obligated to ensure that it is
+    available for as long as needed to satisfy these requirements.
+
+    e) Convey the object code using peer-to-peer transmission, provided
+    you inform other peers where the object code and Corresponding
+    Source of the work are being offered to the general public at no
+    charge under subsection 6d.
+
+  A separable portion of the object code, whose source code is excluded
+from the Corresponding Source as a System Library, need not be
+included in conveying the object code work.
+
+  A "User Product" is either (1) a "consumer product", which means any
+tangible personal property which is normally used for personal, family,
+or household purposes, or (2) anything designed or sold for incorporation
+into a dwelling.  In determining whether a product is a consumer product,
+doubtful cases shall be resolved in favor of coverage.  For a particular
+product received by a particular user, "normally used" refers to a
+typical or common use of that class of product, regardless of the status
+of the particular user or of the way in which the particular user
+actually uses, or expects or is expected to use, the product.  A product
+is a consumer product regardless of whether the product has substantial
+commercial, industrial or non-consumer uses, unless such uses represent
+the only significant mode of use of the product.
+
+  "Installation Information" for a User Product means any methods,
+procedures, authorization keys, or other information required to install
+and execute modified versions of a covered work in that User Product from
+a modified version of its Corresponding Source.  The information must
+suffice to ensure that the continued functioning of the modified object
+code is in no case prevented or interfered with solely because
+modification has been made.
+
+  If you convey an object code work under this section in, or with, or
+specifically for use in, a User Product, and the conveying occurs as
+part of a transaction in which the right of possession and use of the
+User Product is transferred to the recipient in perpetuity or for a
+fixed term (regardless of how the transaction is characterized), the
+Corresponding Source conveyed under this section must be accompanied
+by the Installation Information.  But this requirement does not apply
+if neither you nor any third party retains the ability to install
+modified object code on the User Product (for example, the work has
+been installed in ROM).
+
+  The requirement to provide Installation Information does not include a
+requirement to continue to provide support service, warranty, or updates
+for a work that has been modified or installed by the recipient, or for
+the User Product in which it has been modified or installed.  Access to a
+network may be denied when the modification itself materially and
+adversely affects the operation of the network or violates the rules and
+protocols for communication across the network.
+
+  Corresponding Source conveyed, and Installation Information provided,
+in accord with this section must be in a format that is publicly
+documented (and with an implementation available to the public in
+source code form), and must require no special password or key for
+unpacking, reading or copying.
+
+  7. Additional Terms.
+
+  "Additional permissions" are terms that supplement the terms of this
+License by making exceptions from one or more of its conditions.
+Additional permissions that are applicable to the entire Program shall
+be treated as though they were included in this License, to the extent
+that they are valid under applicable law.  If additional permissions
+apply only to part of the Program, that part may be used separately
+under those permissions, but the entire Program remains governed by
+this License without regard to the additional permissions.
+
+  When you convey a copy of a covered work, you may at your option
+remove any additional permissions from that copy, or from any part of
+it.  (Additional permissions may be written to require their own
+removal in certain cases when you modify the work.)  You may place
+additional permissions on material, added by you to a covered work,
+for which you have or can give appropriate copyright permission.
+
+  Notwithstanding any other provision of this License, for material you
+add to a covered work, you may (if authorized by the copyright holders of
+that material) supplement the terms of this License with terms:
+
+    a) Disclaiming warranty or limiting liability differently from the
+    terms of sections 15 and 16 of this License; or
+
+    b) Requiring preservation of specified reasonable legal notices or
+    author attributions in that material or in the Appropriate Legal
+    Notices displayed by works containing it; or
+
+    c) Prohibiting misrepresentation of the origin of that material, or
+    requiring that modified versions of such material be marked in
+    reasonable ways as different from the original version; or
+
+    d) Limiting the use for publicity purposes of names of licensors or
+    authors of the material; or
+
+    e) Declining to grant rights under trademark law for use of some
+    trade names, trademarks, or service marks; or
+
+    f) Requiring indemnification of licensors and authors of that
+    material by anyone who conveys the material (or modified versions of
+    it) with contractual assumptions of liability to the recipient, for
+    any liability that these contractual assumptions directly impose on
+    those licensors and authors.
+
+  All other non-permissive additional terms are considered "further
+restrictions" within the meaning of section 10.  If the Program as you
+received it, or any part of it, contains a notice stating that it is
+governed by this License along with a term that is a further
+restriction, you may remove that term.  If a license document contains
+a further restriction but permits relicensing or conveying under this
+License, you may add to a covered work material governed by the terms
+of that license document, provided that the further restriction does
+not survive such relicensing or conveying.
+
+  If you add terms to a covered work in accord with this section, you
+must place, in the relevant source files, a statement of the
+additional terms that apply to those files, or a notice indicating
+where to find the applicable terms.
+
+  Additional terms, permissive or non-permissive, may be stated in the
+form of a separately written license, or stated as exceptions;
+the above requirements apply either way.
+
+  8. Termination.
+
+  You may not propagate or modify a covered work except as expressly
+provided under this License.  Any attempt otherwise to propagate or
+modify it is void, and will automatically terminate your rights under
+this License (including any patent licenses granted under the third
+paragraph of section 11).
+
+  However, if you cease all violation of this License, then your
+license from a particular copyright holder is reinstated (a)
+provisionally, unless and until the copyright holder explicitly and
+finally terminates your license, and (b) permanently, if the copyright
+holder fails to notify you of the violation by some reasonable means
+prior to 60 days after the cessation.
+
+  Moreover, your license from a particular copyright holder is
+reinstated permanently if the copyright holder notifies you of the
+violation by some reasonable means, this is the first time you have
+received notice of violation of this License (for any work) from that
+copyright holder, and you cure the violation prior to 30 days after
+your receipt of the notice.
+
+  Termination of your rights under this section does not terminate the
+licenses of parties who have received copies or rights from you under
+this License.  If your rights have been terminated and not permanently
+reinstated, you do not qualify to receive new licenses for the same
+material under section 10.
+
+  9. Acceptance Not Required for Having Copies.
+
+  You are not required to accept this License in order to receive or
+run a copy of the Program.  Ancillary propagation of a covered work
+occurring solely as a consequence of using peer-to-peer transmission
+to receive a copy likewise does not require acceptance.  However,
+nothing other than this License grants you permission to propagate or
+modify any covered work.  These actions infringe copyright if you do
+not accept this License.  Therefore, by modifying or propagating a
+covered work, you indicate your acceptance of this License to do so.
+
+  10. Automatic Licensing of Downstream Recipients.
+
+  Each time you convey a covered work, the recipient automatically
+receives a license from the original licensors, to run, modify and
+propagate that work, subject to this License.  You are not responsible
+for enforcing compliance by third parties with this License.
+
+  An "entity transaction" is a transaction transferring control of an
+organization, or substantially all assets of one, or subdividing an
+organization, or merging organizations.  If propagation of a covered
+work results from an entity transaction, each party to that
+transaction who receives a copy of the work also receives whatever
+licenses to the work the party's predecessor in interest had or could
+give under the previous paragraph, plus a right to possession of the
+Corresponding Source of the work from the predecessor in interest, if
+the predecessor has it or can get it with reasonable efforts.
+
+  You may not impose any further restrictions on the exercise of the
+rights granted or affirmed under this License.  For example, you may
+not impose a license fee, royalty, or other charge for exercise of
+rights granted under this License, and you may not initiate litigation
+(including a cross-claim or counterclaim in a lawsuit) alleging that
+any patent claim is infringed by making, using, selling, offering for
+sale, or importing the Program or any portion of it.
+
+  11. Patents.
+
+  A "contributor" is a copyright holder who authorizes use under this
+License of the Program or a work on which the Program is based.  The
+work thus licensed is called the contributor's "contributor version".
+
+  A contributor's "essential patent claims" are all patent claims
+owned or controlled by the contributor, whether already acquired or
+hereafter acquired, that would be infringed by some manner, permitted
+by this License, of making, using, or selling its contributor version,
+but do not include claims that would be infringed only as a
+consequence of further modification of the contributor version.  For
+purposes of this definition, "control" includes the right to grant
+patent sublicenses in a manner consistent with the requirements of
+this License.
+
+  Each contributor grants you a non-exclusive, worldwide, royalty-free
+patent license under the contributor's essential patent claims, to
+make, use, sell, offer for sale, import and otherwise run, modify and
+propagate the contents of its contributor version.
+
+  In the following three paragraphs, a "patent license" is any express
+agreement or commitment, however denominated, not to enforce a patent
+(such as an express permission to practice a patent or covenant not to
+sue for patent infringement).  To "grant" such a patent license to a
+party means to make such an agreement or commitment not to enforce a
+patent against the party.
+
+  If you convey a covered work, knowingly relying on a patent license,
+and the Corresponding Source of the work is not available for anyone
+to copy, free of charge and under the terms of this License, through a
+publicly available network server or other readily accessible means,
+then you must either (1) cause the Corresponding Source to be so
+available, or (2) arrange to deprive yourself of the benefit of the
+patent license for this particular work, or (3) arrange, in a manner
+consistent with the requirements of this License, to extend the patent
+license to downstream recipients.  "Knowingly relying" means you have
+actual knowledge that, but for the patent license, your conveying the
+covered work in a country, or your recipient's use of the covered work
+in a country, would infringe one or more identifiable patents in that
+country that you have reason to believe are valid.
+
+  If, pursuant to or in connection with a single transaction or
+arrangement, you convey, or propagate by procuring conveyance of, a
+covered work, and grant a patent license to some of the parties
+receiving the covered work authorizing them to use, propagate, modify
+or convey a specific copy of the covered work, then the patent license
+you grant is automatically extended to all recipients of the covered
+work and works based on it.
+
+  A patent license is "discriminatory" if it does not include within
+the scope of its coverage, prohibits the exercise of, or is
+conditioned on the non-exercise of one or more of the rights that are
+specifically granted under this License.  You may not convey a covered
+work if you are a party to an arrangement with a third party that is
+in the business of distributing software, under which you make payment
+to the third party based on the extent of your activity of conveying
+the work, and under which the third party grants, to any of the
+parties who would receive the covered work from you, a discriminatory
+patent license (a) in connection with copies of the covered work
+conveyed by you (or copies made from those copies), or (b) primarily
+for and in connection with specific products or compilations that
+contain the covered work, unless you entered into that arrangement,
+or that patent license was granted, prior to 28 March 2007.
+
+  Nothing in this License shall be construed as excluding or limiting
+any implied license or other defenses to infringement that may
+otherwise be available to you under applicable patent law.
+
+  12. No Surrender of Others' Freedom.
+
+  If conditions are imposed on you (whether by court order, agreement or
+otherwise) that contradict the conditions of this License, they do not
+excuse you from the conditions of this License.  If you cannot convey a
+covered work so as to satisfy simultaneously your obligations under this
+License and any other pertinent obligations, then as a consequence you may
+not convey it at all.  For example, if you agree to terms that obligate you
+to collect a royalty for further conveying from those to whom you convey
+the Program, the only way you could satisfy both those terms and this
+License would be to refrain entirely from conveying the Program.
+
+  13. Use with the GNU Affero General Public License.
+
+  Notwithstanding any other provision of this License, you have
+permission to link or combine any covered work with a work licensed
+under version 3 of the GNU Affero General Public License into a single
+combined work, and to convey the resulting work.  The terms of this
+License will continue to apply to the part which is the covered work,
+but the special requirements of the GNU Affero General Public License,
+section 13, concerning interaction through a network will apply to the
+combination as such.
+
+  14. Revised Versions of this License.
+
+  The Free Software Foundation may publish revised and/or new versions of
+the GNU General Public License from time to time.  Such new versions will
+be similar in spirit to the present version, but may differ in detail to
+address new problems or concerns.
+
+  Each version is given a distinguishing version number.  If the
+Program specifies that a certain numbered version of the GNU General
+Public License "or any later version" applies to it, you have the
+option of following the terms and conditions either of that numbered
+version or of any later version published by the Free Software
+Foundation.  If the Program does not specify a version number of the
+GNU General Public License, you may choose any version ever published
+by the Free Software Foundation.
+
+  If the Program specifies that a proxy can decide which future
+versions of the GNU General Public License can be used, that proxy's
+public statement of acceptance of a version permanently authorizes you
+to choose that version for the Program.
+
+  Later license versions may give you additional or different
+permissions.  However, no additional obligations are imposed on any
+author or copyright holder as a result of your choosing to follow a
+later version.
+
+  15. Disclaimer of Warranty.
+
+  THERE IS NO WARRANTY FOR THE PROGRAM, TO THE EXTENT PERMITTED BY
+APPLICABLE LAW.  EXCEPT WHEN OTHERWISE STATED IN WRITING THE COPYRIGHT
+HOLDERS AND/OR OTHER PARTIES PROVIDE THE PROGRAM "AS IS" WITHOUT WARRANTY
+OF ANY KIND, EITHER EXPRESSED OR IMPLIED, INCLUDING, BUT NOT LIMITED TO,
+THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
+PURPOSE.  THE ENTIRE RISK AS TO THE QUALITY AND PERFORMANCE OF THE PROGRAM
+IS WITH YOU.  SHOULD THE PROGRAM PROVE DEFECTIVE, YOU ASSUME THE COST OF
+ALL NECESSARY SERVICING, REPAIR OR CORRECTION.
+
+  16. Limitation of Liability.
+
+  IN NO EVENT UNLESS REQUIRED BY APPLICABLE LAW OR AGREED TO IN WRITING
+WILL ANY COPYRIGHT HOLDER, OR ANY OTHER PARTY WHO MODIFIES AND/OR CONVEYS
+THE PROGRAM AS PERMITTED ABOVE, BE LIABLE TO YOU FOR DAMAGES, INCLUDING ANY
+GENERAL, SPECIAL, INCIDENTAL OR CONSEQUENTIAL DAMAGES ARISING OUT OF THE
+USE OR INABILITY TO USE THE PROGRAM (INCLUDING BUT NOT LIMITED TO LOSS OF
+DATA OR DATA BEING RENDERED INACCURATE OR LOSSES SUSTAINED BY YOU OR THIRD
+PARTIES OR A FAILURE OF THE PROGRAM TO OPERATE WITH ANY OTHER PROGRAMS),
+EVEN IF SUCH HOLDER OR OTHER PARTY HAS BEEN ADVISED OF THE POSSIBILITY OF
+SUCH DAMAGES.
+
+  17. Interpretation of Sections 15 and 16.
+
+  If the disclaimer of warranty and limitation of liability provided
+above cannot be given local legal effect according to their terms,
+reviewing courts shall apply local law that most closely approximates
+an absolute waiver of all civil liability in connection with the
+Program, unless a warranty or assumption of liability accompanies a
+copy of the Program in return for a fee.
+
+                     END OF TERMS AND CONDITIONS
+
+            How to Apply These Terms to Your New Programs
+
+  If you develop a new program, and you want it to be of the greatest
+possible use to the public, the best way to achieve this is to make it
+free software which everyone can redistribute and change under these terms.
+
+  To do so, attach the following notices to the program.  It is safest
+to attach them to the start of each source file to most effectively
+state the exclusion of warranty; and each file should have at least
+the "copyright" line and a pointer to where the full notice is found.
+
+    <one line to give the program's name and a brief idea of what it does.>
+    Copyright (C) <year>  <name of author>
+
+    This program is free software: you can redistribute it and/or modify
+    it under the terms of the GNU General Public License as published by
+    the Free Software Foundation, either version 3 of the License, or
+    (at your option) any later version.
+
+    This program is distributed in the hope that it will be useful,
+    but WITHOUT ANY WARRANTY; without even the implied warranty of
+    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+    GNU General Public License for more details.
+
+    You should have received a copy of the GNU General Public License
+    along with this program.  If not, see <https://www.gnu.org/licenses/>.
+
+Also add information on how to contact you by electronic and paper mail.
+
+  If the program does terminal interaction, make it output a short
+notice like this when it starts in an interactive mode:
+
+    <program>  Copyright (C) <year>  <name of author>
+    This program comes with ABSOLUTELY NO WARRANTY; for details type `show w'.
+    This is free software, and you are welcome to redistribute it
+    under certain conditions; type `show c' for details.
+
+The hypothetical commands `show w' and `show c' should show the appropriate
+parts of the General Public License.  Of course, your program's commands
+might be different; for a GUI interface, you would use an "about box".
+
+  You should also get your employer (if you work as a programmer) or school,
+if any, to sign a "copyright disclaimer" for the program, if necessary.
+For more information on this, and how to apply and follow the GNU GPL, see
+<https://www.gnu.org/licenses/>.
+
+  The GNU General Public License does not permit incorporating your program
+into proprietary programs.  If your program is a subroutine library, you
+may consider it more useful to permit linking proprietary applications with
+the library.  If this is what you want to do, use the GNU Lesser General
+Public License instead of this License.  But first, please read
+<https://www.gnu.org/licenses/why-not-lgpl.html>.
diff --git a/Makefile b/Makefile
new file mode 100644
index 0000000..a75f9ca
--- /dev/null
+++ b/Makefile
@@ -0,0 +1,54 @@
+# SPDX-License-Identifier: GPL-2.0-or-later
+
+define HELP_TEXT
+
+- test, watch_test
+  Runs all tests.
+
+Environment Variables:
+
+- EMACS_BIN
+  The command used to run Emacs, defaults to "emacs"
+
+endef
+# HELP_TEXT (end)
+
+# Needed for when tests are run from another directory: `make -C ./path/to/tests`.
+BASE_DIR := $(CURDIR)
+
+# Default Emacs binary
+EMACS_BIN ?= emacs
+
+EL_FILES := \
+	./with-command-redo.el \
+	./tests/with-command-redo_tests.el
+
+# Additional files to watch (can be overridden)
+EXTRA_WATCH_FILES ?=
+
+# -----------------------------------------------------------------------------
+# Help for build targets
+
+export HELP_TEXT
+.PHONY: help
+help: FORCE
+	@echo "$$HELP_TEXT"
+
+
+# -----------------------------------------------------------------------------
+# Tests
+
+.PHONY: test
+test: FORCE
+	@cd "$(BASE_DIR)" && \
+	python ./tests/with-command-redo_tests.py
+
+.PHONY: watch_test
+watch_test: FORCE
+	@cd "$(BASE_DIR)" && \
+	bash -c "while true; do \
+		inotifywait -e close_write $(EL_FILES); \
+		tput clear && make test; \
+	done"
+
+FORCE:
diff --git a/changelog.rst b/changelog.rst
new file mode 100644
index 0000000..e4721fe
--- /dev/null
+++ b/changelog.rst
@@ -0,0 +1,8 @@
+
+##########
+Change Log
+##########
+
+- Version 0.1 (2026-04-05)
+
+  Initial release.
diff --git a/readme.rst b/readme.rst
new file mode 100644
index 0000000..5ee0479
--- /dev/null
+++ b/readme.rst
@@ -0,0 +1,80 @@
+#################
+With Command Redo
+#################
+
+A generic mechanism for running a command repeatedly without cluttering your undo history.
+
+Where each successive call undoes the previous result before applying the next.
+Consumers build cycling, completion, or other repeat-with-redo behaviors on top.
+
+Note that this is middle-ware since it's intended for other packages to use.
+
+Available via `melpa <https://melpa.org/#/with-command-redo>`__.
+
+
+Usage
+=====
+
+This package exposes:
+
+- ``with-command-redo`` macro.
+- ``with-command-redo-fn`` function variant.
+- ``with-command-redo-active-p`` query if a redo-chain is active, takes a single ``id`` symbol.
+
+
+Arguments
+---------
+
+Both ``with-command-redo`` and ``with-command-redo-fn`` accept:
+
+``:id SYMBOL``
+   Identifies the chain. Multiple commands sharing the same id
+   continue each other's chain. Required.
+``:on-other-command FUNCTION``
+   Called from ``post-command-hook`` when a non-modifying external command
+   runs while the chain is active. Receives the cache as its sole argument.
+   Side effects (messaging, cache mutation) are permitted.
+   Return non-nil to break the chain, nil to keep it alive.
+
+The body (macro) or callback (function) receives a plist with:
+
+``:count``
+   The execution count (0 on the first call).
+``:cache``
+   nil on the first call. Use ``plist-put`` to pass a value to the next call.
+``:result``
+   Defaults to t. Use ``plist-put`` to set nil when the operation has no result.
+
+
+Example
+-------
+
+Cycle through a list of strings, each call undoes the previous insertion:
+
+.. code-block:: elisp
+
+   ;; Macro variant.
+   (defun my-cycle-insert ()
+     (interactive)
+     (with-command-redo (list :id 'my-cycle) props
+       (let ((count (plist-get props :count))
+             (items '("alpha" "beta" "gamma")))
+         (insert (nth (mod count (length items)) items)))))
+
+   ;; Function variant (for conditional use without macro expansion).
+   (defun my-cycle-insert ()
+     (interactive)
+     (with-command-redo-fn
+      (list :id 'my-cycle)
+      (lambda (props)
+        (let ((count (plist-get props :count))
+              (items '("alpha" "beta" "gamma")))
+          (insert (nth (mod count (length items)) items))))))
+
+
+Installation
+============
+
+.. code-block:: elisp
+
+   (use-package with-command-redo)
diff --git a/tests/with-command-redo_tests.el b/tests/with-command-redo_tests.el
new file mode 100644
index 0000000..c222797
--- /dev/null
+++ b/tests/with-command-redo_tests.el
@@ -0,0 +1,327 @@
+;;; with-command-redo_tests.el --- With command redo test -*- lexical-binding: t -*-
+
+;; SPDX-License-Identifier: GPL-2.0-or-later
+;; Copyright (C) 2026  Campbell Barton
+
+;; Author: Campbell Barton <ideasman42@gmail.com>
+
+;; URL: https://codeberg.org/ideasman42/emacs-with-command-redo
+;; Keywords: convenience
+;; Version: 0.1
+;; Package-Requires: ((emacs "29.1"))
+
+;;; Commentary:
+
+;; This is a test for `with-command-redo'.
+;;
+
+;;; Usage
+
+;;
+;; To test this file run:
+;;
+;;     `python tests/with-command-redo_tests.py'
+;;
+
+;;; Code:
+
+(require 'ert)
+
+;; ---------------------------------------------------------------------------
+;; Setup Environment
+
+;; Loaded by the Python test runner which pre-loads `with-command-redo'.
+
+;; ---------------------------------------------------------------------------
+;; Test Utilities
+
+(defmacro simulate-input (&rest keys)
+  "Helper macro to simulate input using KEYS."
+  (declare (indent 0))
+  `(let ((keys-list (list ,@keys)))
+     (dolist (keys keys-list)
+       (let ((minibuffer-message-timeout 0))
+         (execute-kbd-macro keys)))))
+
+(defun buffer-reset-text (initial-buffer-text)
+  "Use INITIAL-BUFFER-TEXT to initialize the buffer with text."
+  (buffer-disable-undo)
+  (erase-buffer)
+  (save-excursion (insert initial-buffer-text))
+  (buffer-enable-undo))
+
+(defmacro with-command-redo-test--run (initial-buffer-text command &rest body)
+  "Run BODY in a buffer with INITIAL-BUFFER-TEXT, binding M-p to COMMAND.
+Messages are suppressed."
+  (declare (indent 2))
+  `(let ((buf (generate-new-buffer "with-command-redo-test")))
+     (switch-to-buffer buf)
+     (buffer-reset-text ,initial-buffer-text)
+     (let ((inhibit-message t))
+       (local-set-key (kbd "M-p") ,command)
+       ,@body)
+     (kill-buffer buf)))
+
+;; ---------------------------------------------------------------------------
+;; Test Commands
+
+(defun with-command-redo-test--cycle-insert ()
+  "Insert cycling text: alpha, beta, gamma on successive calls."
+  (interactive)
+  (with-command-redo (list :id 'test-cycle) props
+    (let ((count (plist-get props :count))
+          (items '("alpha" "beta" "gamma")))
+      (insert (nth (mod count (length items)) items)))))
+
+(defun with-command-redo-test--cycle-insert-with-cache ()
+  "Insert cycling text, using cache to track items."
+  (interactive)
+  (with-command-redo (list :id 'test-cache) props
+    (let ((count (plist-get props :count))
+          (cache (plist-get props :cache)))
+      (unless cache
+        (setq cache '("one" "two" "three"))
+        (plist-put props :cache cache))
+      (insert (nth (mod count (length cache)) cache)))))
+
+(defun with-command-redo-test--insert-with-result ()
+  "Insert text only on even calls, odd calls produce no result."
+  (interactive)
+  (with-command-redo (list :id 'test-result) props
+    (let ((count (plist-get props :count)))
+      (when (= (mod count 2) 0)
+        (insert "even")
+        (plist-put props :result t))
+      (plist-put props :result (= (mod count 2) 0)))))
+
+(defun with-command-redo-test--cycle-insert-other ()
+  "Insert cycling text with a different chain id."
+  (interactive)
+  (with-command-redo (list :id 'test-cycle-other) props
+    (let ((count (plist-get props :count))
+          (items '("one" "two" "three")))
+      (insert (nth (mod count (length items)) items)))))
+
+(defun with-command-redo-test--cycle-insert-at-point ()
+  "Insert cycling text at point, for testing point restoration."
+  (interactive)
+  (with-command-redo (list :id 'test-point) props
+    (let ((count (plist-get props :count))
+          (items '("[first]" "[second]" "[third]")))
+      (insert (nth (mod count (length items)) items)))))
+
+(defun with-command-redo-test--cycle-with-break-p ()
+  "Insert cycling text, allowing `beginning-of-buffer' without breaking."
+  (interactive)
+  (with-command-redo
+      (list :id 'test-break-p
+            :on-other-command (lambda (_cache) (not (eq this-command 'beginning-of-buffer))))
+      props
+    (let ((count (plist-get props :count))
+          (items '("alpha" "beta" "gamma")))
+      (insert (nth (mod count (length items)) items)))))
+
+;; ---------------------------------------------------------------------------
+;; Tests: Single Call
+
+(ert-deftest single-call ()
+  "A single call should insert text."
+  (with-command-redo-test--run "" #'with-command-redo-test--cycle-insert
+    (simulate-input
+      (kbd "M-p"))
+    (should (equal "alpha" (buffer-substring-no-properties (point-min) (point-max))))))
+
+;; ---------------------------------------------------------------------------
+;; Tests: Chain Cycling
+
+(ert-deftest chain-two-calls ()
+  "Second call should undo the first and insert the next item."
+  (with-command-redo-test--run "" #'with-command-redo-test--cycle-insert
+    (simulate-input
+      (kbd "M-p M-p"))
+    (should (equal "beta" (buffer-substring-no-properties (point-min) (point-max))))))
+
+(ert-deftest chain-three-calls ()
+  "Three calls should cycle to the third item."
+  (with-command-redo-test--run "" #'with-command-redo-test--cycle-insert
+    (simulate-input
+      (kbd "M-p M-p M-p"))
+    (should (equal "gamma" (buffer-substring-no-properties (point-min) (point-max))))))
+
+(ert-deftest chain-wraps-around ()
+  "Four calls should wrap back to the first item."
+  (with-command-redo-test--run "" #'with-command-redo-test--cycle-insert
+    (simulate-input
+      (kbd "M-p M-p M-p M-p"))
+    (should (equal "alpha" (buffer-substring-no-properties (point-min) (point-max))))))
+
+;; ---------------------------------------------------------------------------
+;; Tests: Existing Buffer Content
+
+(ert-deftest preserves-existing-text ()
+  "Chain should not disturb text that existed before the chain."
+  (with-command-redo-test--run "prefix " #'with-command-redo-test--cycle-insert
+    (goto-char (point-max))
+    (simulate-input
+      (kbd "M-p M-p"))
+    (should (equal "prefix beta" (buffer-substring-no-properties (point-min) (point-max))))))
+
+;; ---------------------------------------------------------------------------
+;; Tests: Cache
+
+(ert-deftest cache-persists ()
+  "Cache set in the first call should be available in subsequent calls."
+  (with-command-redo-test--run "" #'with-command-redo-test--cycle-insert-with-cache
+    (simulate-input
+      (kbd "M-p M-p"))
+    (should (equal "two" (buffer-substring-no-properties (point-min) (point-max))))))
+
+;; ---------------------------------------------------------------------------
+;; Tests: Result Flag
+
+(ert-deftest result-nil-no-chain ()
+  "When result is nil the chain should not be established."
+  (with-command-redo-test--run "" #'with-command-redo-test--insert-with-result
+    ;; First call (count=0, even) inserts "even", chain saved.
+    ;; Second call (count=1, odd) undoes "even", result is nil, chain dropped.
+    ;; Third call (count=0, fresh chain) inserts "even".
+    (simulate-input
+      (kbd "M-p M-p M-p"))
+    (should (equal "even" (buffer-substring-no-properties (point-min) (point-max))))))
+
+;; ---------------------------------------------------------------------------
+;; Tests: Different ID Breaks Chain
+
+(ert-deftest different-id-breaks-chain ()
+  "Switching to a command with a different :id should break the chain."
+  (with-command-redo-test--run "" #'with-command-redo-test--cycle-insert
+    (local-set-key (kbd "M-n") #'with-command-redo-test--cycle-insert-other)
+    ;; M-p inserts "alpha" (chain A), M-p cycles to "beta" (chain A),
+    ;; M-n has a different id so starts fresh, inserts "one" without undoing "beta".
+    (simulate-input
+      (kbd "M-p M-p M-n"))
+    (should (equal "betaone" (buffer-substring-no-properties (point-min) (point-max))))))
+
+;; ---------------------------------------------------------------------------
+;; Tests: External Modification Breaks Chain
+
+(ert-deftest external-edit-breaks-chain ()
+  "An external buffer modification should break the chain."
+  (with-command-redo-test--run "" #'with-command-redo-test--cycle-insert
+    ;; Bind M-n to a plain insert (external modification).
+    (local-set-key
+     (kbd "M-n")
+     (lambda ()
+       (interactive)
+       (insert "EXT")))
+    ;; M-p inserts "alpha", M-n inserts "EXT" (breaks chain via before-change-hook),
+    ;; M-p starts fresh chain, inserts "alpha" again.
+    (simulate-input
+      (kbd "M-p M-n M-p"))
+    (should (equal "alphaEXTalpha" (buffer-substring-no-properties (point-min) (point-max))))))
+
+;; ---------------------------------------------------------------------------
+;; Tests: On Other Command Handler
+
+(ert-deftest on-other-command-keeps-chain ()
+  "A command allowed by :on-other-command should not break the chain."
+  (with-command-redo-test--run "" #'with-command-redo-test--cycle-with-break-p
+    ;; Bind M-n to `beginning-of-buffer' which the handler allows.
+    (local-set-key (kbd "M-n") #'beginning-of-buffer)
+    ;; M-p inserts "alpha", M-n runs beginning-of-buffer (allowed, chain continues),
+    ;; M-p cycles to "beta".
+    (simulate-input
+      (kbd "M-p M-n M-p"))
+    (should (equal "beta" (buffer-substring-no-properties (point-min) (point-max))))))
+
+(ert-deftest on-other-command-breaks-chain ()
+  "A command not allowed by :on-other-command should break the chain."
+  (with-command-redo-test--run "" #'with-command-redo-test--cycle-with-break-p
+    ;; Bind M-n to `end-of-buffer' which the handler does not allow.
+    (local-set-key (kbd "M-n") #'end-of-buffer)
+    ;; M-p inserts "alpha", M-n runs end-of-buffer (not allowed, chain breaks),
+    ;; M-p starts fresh, inserts "alpha" again (not "beta").
+    (simulate-input
+      (kbd "M-p M-n M-p"))
+    (should (equal "alphaalpha" (buffer-substring-no-properties (point-min) (point-max))))))
+
+;; ---------------------------------------------------------------------------
+;; Tests: Point Restoration
+
+(ert-deftest point-restored-between-calls ()
+  "Point should be restored to its pre-chain position before each redo."
+  (with-command-redo-test--run "abcd" #'with-command-redo-test--cycle-insert-at-point
+    ;; Place point between "ab" and "cd".
+    (goto-char 3)
+    ;; M-p inserts "[first]" at point 3 -> "ab[first]cd".
+    ;; M-p undoes, restores point to 3, inserts "[second]" -> "ab[second]cd".
+    (simulate-input
+      (kbd "M-p M-p"))
+    (should (equal "ab[second]cd" (buffer-substring-no-properties (point-min) (point-max))))))
+
+;; ---------------------------------------------------------------------------
+;; Tests: Undo After Chain
+
+(ert-deftest undo-after-chain ()
+  "After the chain ends, undo should cleanly restore the original buffer."
+  (with-command-redo-test--run "original" #'with-command-redo-test--cycle-insert
+    (goto-char (point-max))
+    ;; M-p inserts "alpha", M-p cycles to "beta".
+    (simulate-input
+      (kbd "M-p M-p"))
+    (should (equal "originalbeta" (buffer-substring-no-properties (point-min) (point-max))))
+    ;; Now break the chain with a non-chain command, then undo.
+    ;; beginning-of-buffer breaks the chain, then undo should remove "beta".
+    (local-set-key (kbd "M-n") #'beginning-of-buffer)
+    (local-set-key (kbd "M-u") #'undo)
+    (simulate-input
+      (kbd "M-n M-u"))
+    (should (equal "original" (buffer-substring-no-properties (point-min) (point-max))))))
+
+;; ---------------------------------------------------------------------------
+;; Tests: Undo Disabled
+
+(ert-deftest undo-disabled-signals-error ()
+  "Calling the macro in a buffer with undo disabled should signal a user-error."
+  (with-command-redo-test--run "" #'with-command-redo-test--cycle-insert
+    (buffer-disable-undo)
+    (should-error
+     (with-command-redo-test--cycle-insert)
+     :type 'user-error)))
+
+;; ---------------------------------------------------------------------------
+;; Test Commands: Function Variant
+
+(defun with-command-redo-test--fn-cycle-insert ()
+  "Insert cycling text using `with-command-redo-fn'."
+  (interactive)
+  (with-command-redo-fn
+   (list :id 'test-fn-cycle)
+   (lambda (props)
+     (let ((count (plist-get props :count))
+           (items '("alpha" "beta" "gamma")))
+       (insert (nth (mod count (length items)) items))))))
+
+;; ---------------------------------------------------------------------------
+;; Tests: Function Variant
+
+(ert-deftest fn-single-call ()
+  "A single call via `with-command-redo-fn' should insert text."
+  (with-command-redo-test--run "" #'with-command-redo-test--fn-cycle-insert
+    (simulate-input
+      (kbd "M-p"))
+    (should (equal "alpha" (buffer-substring-no-properties (point-min) (point-max))))))
+
+(ert-deftest fn-chain-two-calls ()
+  "Second call via `with-command-redo-fn' should undo the first and insert the next."
+  (with-command-redo-test--run "" #'with-command-redo-test--fn-cycle-insert
+    (simulate-input
+      (kbd "M-p M-p"))
+    (should (equal "beta" (buffer-substring-no-properties (point-min) (point-max))))))
+
+(provide 'with-command-redo_tests)
+;; Local Variables:
+;; fill-column: 99
+;; indent-tabs-mode: nil
+;; End:
+;;; with-command-redo_tests.el ends here
diff --git a/tests/with-command-redo_tests.py b/tests/with-command-redo_tests.py
new file mode 100644
index 0000000..c22b475
--- /dev/null
+++ b/tests/with-command-redo_tests.py
@@ -0,0 +1,41 @@
+# SPDX-License-Identifier: GPL-2.0-or-later
+
+import subprocess
+import os
+import sys
+
+
+THIS_DIR = os.path.normpath(os.path.abspath(os.path.join(os.path.dirname(__file__))))
+BASE_DIR = os.path.normpath(os.path.join(THIS_DIR, ".."))
+
+EMACS_BIN = os.environ.get("EMACS_BIN") or "emacs"
+
+
+def run_with_command_redo_tests() -> int:
+    cmd = [
+        EMACS_BIN,
+        "-batch",
+        "-l", os.path.join(BASE_DIR, "with-command-redo.el"),
+        "-l", os.path.join(THIS_DIR, "with-command-redo_tests.el"),
+        "-f", "ert-run-tests-batch-and-exit"
+    ]
+
+    process = subprocess.Popen(
+        cmd,
+        stdout=subprocess.PIPE,
+        stderr=subprocess.STDOUT,
+        text=True,
+    )
+    for line in process.stdout:
+        sys.stdout.write(line)
+        sys.stdout.flush()
+
+    return process.wait()
+
+
+def main() -> int:
+    return run_with_command_redo_tests()
+
+
+if __name__ == "__main__":
+    sys.exit(main())
diff --git a/with-command-redo.el b/with-command-redo.el
new file mode 100644
index 0000000..63086f4
--- /dev/null
+++ b/with-command-redo.el
@@ -0,0 +1,305 @@
+;;; with-command-redo.el --- Repeat commands with automatic undo -*- lexical-binding: t -*-
+
+;; SPDX-License-Identifier: GPL-2.0-or-later
+;; Copyright (C) 2026  Campbell Barton
+
+;; Author: Campbell Barton <ideasman42@gmail.com>
+
+;; URL: https://codeberg.org/ideasman42/emacs-with-command-redo
+;; Version: 0.1
+;; Package-Requires: ((emacs "29.1"))
+
+;;; Commentary:
+
+;; A generic mechanism for running a command repeatedly where each
+;; successive call undoes the previous result before applying the next.
+;; Consumers build cycling, completion, or other repeat-with-redo
+;; behaviors on top.
+
+;;; Code:
+
+
+;; ---------------------------------------------------------------------------
+;; Internal Variables
+
+(defvar with-command-redo--alist nil
+  "Internal state for the active command-redo chain.
+The global value must remain nil, use as a buffer-local variable only.
+
+Keys are:
+- `buffer-undo-list': The `buffer-undo-list' before execution.
+- `buffer-undo-list-post': The `buffer-undo-list' after execution.
+- `pending-undo-list': The `pending-undo-list' before execution.
+- `point': The point before execution.
+- `chain-id': Symbol identifying the chain.
+- `exec-count': Number of times the callback has been called (0-indexed).
+- `fn-cache': Optional cache for the callback to use.
+- `is-first-post-command': Flag to allow the chain's own command.
+- `on-other-command': Handler for non-modifying external commands.")
+
+
+;; ---------------------------------------------------------------------------
+;; Param Parsing
+
+(defun with-command-redo--parse-params (params)
+  "Parse keyword PARAMS, return an alist of parsed values."
+  (declare (important-return-value t))
+  (let ((kw-id nil)
+        (kw-on-other-command nil)
+        (keyw nil)
+        (val nil)
+        (params-rest params))
+
+    (unless (listp params-rest)
+      (error "with-command-redo: PARAMS must be a list"))
+
+    (while (keywordp (setq keyw (car params-rest)))
+      (setq params-rest (cdr params-rest))
+      (setq val (pop params-rest))
+      (pcase keyw
+        (:id (setq kw-id val))
+        (:on-other-command (setq kw-on-other-command val))
+        (_ (error "With-command-redo: unknown keyword %S" keyw))))
+
+    (when params-rest
+      (error "With-command-redo: unexpected trailing arguments in PARAMS: %S" params-rest))
+
+    (unless kw-id
+      (error "With-command-redo: :id is required"))
+
+    (list (cons 'id kw-id) (cons 'on-other-command kw-on-other-command))))
+
+
+;; ---------------------------------------------------------------------------
+;; Internal Utilities
+
+(defun with-command-redo--buffer-undo-skip-barrier (list)
+  "Skip leading nil boundaries in LIST.
+
+Argument LIST is a `buffer-undo-list' compatible list."
+  (declare (important-return-value t))
+  (while (and list (null (car list)))
+    (setq list (cdr list)))
+  list)
+
+(defun with-command-redo--undo-next (list)
+  "Get the next undo step in LIST.
+
+Argument LIST is a `buffer-undo-list' compatible list."
+  (declare (important-return-value t))
+  (while (car list)
+    (setq list (cdr list)))
+  (with-command-redo--buffer-undo-skip-barrier list))
+
+
+;; ---------------------------------------------------------------------------
+;; Hook Management
+
+(defun with-command-redo--hooks-add ()
+  "Add the post-command hook for the command-redo chain (buffer-local)."
+  (declare (important-return-value nil))
+  (add-hook 'post-command-hook #'with-command-redo--post-command-hook 0 t))
+
+(defun with-command-redo--hooks-remove ()
+  "Remove the post-command hook for the command-redo chain (buffer-local)."
+  (declare (important-return-value nil))
+  (remove-hook 'post-command-hook #'with-command-redo--post-command-hook t))
+
+
+;; ---------------------------------------------------------------------------
+;; Hooks
+
+(defun with-command-redo--post-command-hook ()
+  "Post-command hook for the command-redo chain.
+On the chain's own command: clear `is-first-post-command' flag.
+On an external command that modified the buffer: break unconditionally.
+On a non-modifying external command: call `on-other-command',
+break the chain if it returns non-nil."
+  (declare (important-return-value nil))
+  (cond
+   ;; The chain's own command just ran: clear the flag, keep hooks alive.
+   ((alist-get 'is-first-post-command with-command-redo--alist)
+    (setf (alist-get 'is-first-post-command with-command-redo--alist) nil))
+
+   ;; External buffer modification: always break the chain.
+   ((not
+     (eq
+      (with-command-redo--buffer-undo-skip-barrier buffer-undo-list)
+      (alist-get 'buffer-undo-list-post with-command-redo--alist)))
+    (with-command-redo--hooks-remove)
+    (kill-local-variable 'with-command-redo--alist))
+
+   ;; A non-modifying external command ran while chain is active.
+   (t
+    (let ((on-other-command (alist-get 'on-other-command with-command-redo--alist)))
+      (when (or (null on-other-command)
+                (funcall on-other-command (alist-get 'fn-cache with-command-redo--alist)))
+        (with-command-redo--hooks-remove)
+        (kill-local-variable 'with-command-redo--alist))))))
+
+
+;; ---------------------------------------------------------------------------
+;; Public API
+
+;;;###autoload
+(defmacro with-command-redo (params props-var &rest body)
+  "Execute BODY with undo-and-redo chain management.
+Expands to a call to `with-command-redo-fn', see that function for details.
+
+PARAMS is an expression that evaluates to a plist (:id, :on-other-command).
+PROPS-VAR is a symbol naming the plist bound in BODY.
+
+Return value: the last form in BODY."
+  (declare (indent 2))
+  (unless (symbolp props-var)
+    (error "with-command-redo: PROPS-VAR must be a symbol"))
+  `(with-command-redo-fn ,params (lambda (,props-var) ,@body)))
+
+;;;###autoload
+(defun with-command-redo-fn (params fn)
+  "Function variant of `with-command-redo'.
+
+PARAMS is a plist of keyword arguments:
+
+  :id SYMBOL
+    Identifies the chain.  Required.
+
+  :on-other-command FUNCTION
+    Called from `post-command-hook' when a non-modifying external
+    command runs while the chain is active.  Receives the cache as
+    its sole argument.  Side effects (messaging, cache mutation)
+    are permitted.  Return non-nil to break the chain, nil to keep
+    it alive.
+
+FN is called with a single plist argument containing:
+
+  :count  The execution count (0 on the first call).
+  :cache  nil on the first call.  Use `plist-put' to pass
+          a value to the next call.
+  :result Non-nil when the operation produced a result worth
+          keeping (defaults to t).  Use `plist-put' to set nil
+          when the operation has no result.
+
+Note: only use `plist-put' to update existing keys.
+Adding new keys requires `setq' on the return value which
+won't be visible to the caller.
+
+Return value: forwarded from FN."
+  (declare (important-return-value t))
+
+  (let* ((parsed (with-command-redo--parse-params params))
+         (chain-id (alist-get 'id parsed))
+         (on-other-command (alist-get 'on-other-command parsed)))
+
+    ;; Undo must be enabled for the chain to work.
+    (when (eq buffer-undo-list t)
+      (user-error "With-command-redo: undo disabled for this buffer"))
+
+    (let ((buffer-undo-list-init buffer-undo-list)
+          (pending-undo-list-init pending-undo-list)
+          (exec-count 0)
+          (fn-cache nil)
+
+          ;; Initial values if not overwritten by the values in the alist.
+          (point-init (point)))
+
+      ;; Roll-back and continue the chain.
+      (let ((alist with-command-redo--alist))
+
+        ;; Always clear immediately; reusing after an error could cause
+        ;; unpredictable behavior.
+        (kill-local-variable 'with-command-redo--alist)
+
+        ;; Break the chain if the chain-id changed.
+        (when (and alist (null (eq chain-id (alist-get 'chain-id alist))))
+          (setq alist nil))
+
+        (when alist
+
+          ;; Update vars from previous state.
+          (setq point-init (alist-get 'point alist))
+          (setq buffer-undo-list-init (alist-get 'buffer-undo-list alist))
+          (setq pending-undo-list-init (alist-get 'pending-undo-list alist))
+          (setq fn-cache (alist-get 'fn-cache alist))
+          (setq exec-count (1+ (alist-get 'exec-count alist)))
+
+          ;; Undo with strict checks so we know _exactly_ what's going on
+          ;; and don't allow some unknown state to be entered.
+          (let ((undo-data (cdr buffer-undo-list)) ; Skip the 'nil' car of the list.
+                (undo-data-init (cdr buffer-undo-list-init)))
+
+            ;; It's possible the last action did not add an undo step.
+            ;; This can happen when the callback produces no change.
+            (unless (eq undo-data-init undo-data)
+              ;; Ensure we have exactly one undo step added,
+              ;; so calling undo returns to a known state.
+              (unless (eq undo-data-init (with-command-redo--undo-next undo-data))
+                (user-error "With-command-redo: unexpected undo-state before undo, abort!"))
+
+              ;; Roll back the edit.
+              (let ((this-command nil)
+                    (undo-in-region nil)
+                    (inhibit-message t)
+                    (message-log-max nil))
+
+                (undo-only)
+
+                ;; Ensure a single undo step was rolled back.
+                (setq undo-data (cdr buffer-undo-list))
+                (unless (eq
+                         undo-data-init
+                         (with-command-redo--undo-next (with-command-redo--undo-next undo-data)))
+                  (user-error "With-command-redo: unexpected undo-state after undo, abort!")))))
+
+          ;; Roll back the buffer state.
+          (setq buffer-undo-list buffer-undo-list-init)
+          (setq pending-undo-list pending-undo-list-init)
+
+          (goto-char point-init)))
+
+      ;; Invoke the body with undo amalgamation.
+      (let* ((props (list :count exec-count :cache fn-cache :result t))
+             (body-result
+              (with-undo-amalgamate
+                (funcall fn props))))
+
+        (cond
+         ((null (plist-get props :result))
+          ;; Failure, nothing happened.
+          body-result)
+
+         (t
+          ;; Save state for the next chain call.
+          (make-local-variable 'with-command-redo--alist)
+          (setq with-command-redo--alist
+                (list
+                 (cons 'buffer-undo-list buffer-undo-list-init)
+                 (cons
+                  'buffer-undo-list-post
+                  (with-command-redo--buffer-undo-skip-barrier buffer-undo-list))
+                 (cons 'pending-undo-list pending-undo-list-init)
+                 (cons 'point point-init)
+                 (cons 'chain-id chain-id)
+                 (cons 'exec-count exec-count)
+                 (cons 'fn-cache (plist-get props :cache))
+                 (cons 'is-first-post-command t)
+                 (cons 'on-other-command on-other-command)))
+
+          (with-command-redo--hooks-add)
+
+          ;; Return the body's result.
+          body-result))))))
+
+;;;###autoload
+(defun with-command-redo-active-p (id)
+  "Return non-nil if a chain with ID is active in the current buffer."
+  (declare (important-return-value t))
+  (and (local-variable-p 'with-command-redo--alist)
+       (eq id (alist-get 'chain-id with-command-redo--alist))))
+
+(provide 'with-command-redo)
+;; Local Variables:
+;; fill-column: 99
+;; indent-tabs-mode: nil
+;; End:
+;;; with-command-redo.el ends here