Add incremental RST-to-MyST swap mechanism (#1857)

* feat: add swap_sources.py for incremental RST-to-MyST migration

Pre-build swap/restore script that renames md-{name}.md → {name}.md
before Sphinx builds and restores after. Includes state tracking,
exclude file generation, collision detection, and partial-failure
rollback. 10 tests cover all specified behaviors plus rollback path.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

* feat: add import_myst.py for importing MyST files from myst/* branches

Adds scripts/import_myst.py with import_page, git_show, list_myst_files,
list_rst_files, and do_import. Imported files are written as md-{name}.md
alongside existing RST files; importing is decoupled from swap activation.

Adds tests/test_import_myst.py covering single-page write, identical-skip,
warn-on-different-without-force, force-overwrite, and nested-path creation.
All 5 tests pass on Python 3.9.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

* feat: add MyST swap exclude patterns and directive config to conf.py

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* feat: add swap-wrapped rendering targets to Makefile

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* feat: add swap pre/post build hooks for ReadTheDocs

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* feat: add empty _swap.txt, remove atexit from swap script

The atexit handler in --swap mode caused immediate restore on process
exit, breaking standalone usage. Makefile trap and RTD post_build
handle restore reliably.

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* feat: activate quick-start as MyST canary via swap mechanism

Imports docs/md-quick-start.md from origin/myst/current and adds
quick-start to docs/_swap.txt. Validates the swap pipeline end-to-end
on one page: import_myst pulls the MD via git show, swap_sources
renames md-quick-start.md to quick-start.md, sphinx-build renders
quick-start.html with zero MD-specific warnings, and restore reverses
the rename cleanly.

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* feat: activate 106 visual-validated canaries via swap

Imports 105 MD files (plus quick-start already present) from
origin/myst/current and adds them to docs/_swap.txt. The selection
is the BackstopJS visual-passers cohort: pages with <5% rendered
diff vs the live RST docs at docs.vyos.io/en/latest/, filtered to
those with an RST counterpart on current and no cmdincludemd usage
(template-format reconciliation pending).

Local sphinx-build with all 106 swapped: succeeded with 100
warnings (vs 95 baseline). The 5 new warnings are all undefined
cross-reference labels, not build failures:
- contributing/development.md (missing 'coding-guidelines')
- operation/upgrade-recovery.md (3 missing 'how_it_works' /
  'cancelling_recovery')
- vpp/configuration/dataplane/{buffers,memory,unix}.md (missing
  'vpp_config_dataplane_*' labels)

Source list: ~/.claude/projects/-Users-vybot-GitHub-vyos-documentation/docs/2026-04-29-myst-conversion-audit/visual-passers-under-5pct.txt
BackstopJS report: claude/gifted-hertz-74b9f9 worktree
(visual-compare/), 2026-04-23 vs vyos--1838.org.readthedocs.build.

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* fix: re-import 4 canary md-*.md files with xref label fixes

Re-imports the dash-form-corrected versions of:
- contributing/md-development.md (added (coding-guidelines)= anchor)
- operation/md-upgrade-recovery.md (3 ref renames: how_it_works /
  cancelling_recovery -> dash form)
- vpp/configuration/dataplane/md-buffers.md (vpp_config_dataplane_physmem
  -> vpp-config-dataplane-physmem)
- vpp/configuration/dataplane/md-unix.md
  (vpp_config_dataplane_interface_rx_mode
  -> vpp-config-dataplane-interface-rx-mode)

Source: origin/myst/current commit 59fbe3ea. Verified locally: clean
swap-build no longer reports any of the 5 target labels (1 of 6 —
vpp-config-hugepages — remains because system.md isn't in the canary
swap list; that anchor lives there).

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* fix: re-add 4 canary md-*.md files deleted by 242b334a

Commit 242b334a accidentally staged deletions instead of modifications
because the working tree had unprefixed *.md files left over from an
incomplete swap-restore cycle. Re-imports the same 4 files from
origin/myst/current with the xref label fixes applied:

- contributing/md-development.md       — (coding-guidelines)= anchor
- operation/md-upgrade-recovery.md     — how_it_works → how-it-works,
                                         cancelling_recovery → cancelling-recovery
- vpp/configuration/dataplane/md-buffers.md — vpp_config_dataplane_physmem
                                              → vpp-config-dataplane-physmem
- vpp/configuration/dataplane/md-unix.md   — vpp_config_dataplane_interface_rx_mode
                                              → vpp-config-dataplane-interface-rx-mode

Source: origin/myst/current commit 59fbe3ea.

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* fix: resolve remaining xref label gaps in swap-active build

Three small additions clear the cross-reference warnings tied to
underscore-vs-dash label form mismatches and the vpp-config-hugepages
reference that previously needed system.md in the canary set.

- system.rst: add .. _vpp-config-hugepages: alongside the existing
  underscore label so memory.md references resolve regardless of
  whether system.md is swap-active.
- md-lcp.md: add (vpp_config_dataplane_lcp_ignore-kernel-routes)=
  alongside dash form (carries upstream from myst/current 079fa786).
- md-memory.md: add (vpp_config_dataplane_memory)= alongside dash
  form (also from myst/current 079fa786).

Local clean swap-build with 106 canaries:
  before: 305 warnings, 8 undefined-label entries in our scope
  after:  300 warnings, 0 undefined-label entries in our scope

Remaining undefined-label warnings (release-notes, prepare_commit)
are in documentation.rst and unrelated to the canary swap mechanism.

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* fix: re-add md-lcp.md and md-memory.md (deleted by 870c9e7e)

Same disaster pattern as 242b334a: a swap-restore cycle left
unprefixed *.md files in the working tree, and the subsequent
git add staged deletions instead of modifications. Restoring the
two affected md-*.md files from origin/myst/current 079fa786
(which has the dual underscore+dash anchors needed for the
swap-active build).

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* feat: expand canaries to 114; refresh 3 with cfgcmd body fix

Adds 8 new visual-validated canaries from the post-cfgcmd-fix
BackstopJS run (2026-04-29):

- configuration/policy/as-path-list
- configuration/policy/community-list
- configuration/policy/extcommunity-list
- configuration/policy/large-community-list
- configuration/policy/local-route
- configuration/policy/prefix-list
- configuration/service/salt-minion
- configuration/system/updates

Refreshes 3 existing canaries whose MD content changed via the
cfgcmd/opcmd single-line body fix on myst/current fc19ab5c:

- configuration/firewall/global-options
- configuration/firewall/groups
- configuration/policy/route

All 11 sourced from origin/myst/current. Net: 106 -> 114 canaries.

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* fix: re-import md-cloud-init.md (block 3 fix from myst/current)

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* feat(swap): import .md files and webp transition from myst/current

Selective import from origin/myst/current (cf9c9b34):
- Add/update 255 .md files (full MyST conversion plus webp ref updates)
- Delete 175 PNG/JPG from docs/_static/images (webp twins already present)
- Delete 5 autotest topology.png (webp twins already present)

Preserved on swap (untouched):
- All .rst files (incremental swap pattern)
- conf.py, _ext/, _include/*.txt, .gitignore
- 115 canary md-*.md files
- 7 superpowers/specs/*.md design docs
- Logos vyos-logo.png / vyos-logo-icon.png (referenced by conf.py)

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* chore(swap): remove canary md-*.md files and docs/superpowers

- Remove 115 canary md-*.md files (incremental swap helpers no longer needed)
- Remove 8 files under docs/superpowers (project planning/design docs that
  shouldn't ship in the documentation tree)

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* docs: address Copilot review feedback on imported MyST pages

Fix issues flagged by Copilot review on PR #1857 (the same content lives
in myst/current as the canonical source):

Real bugs:
- site-2-site-cisco.md: replace curly quote (U+2019) with ASCII apostrophe
- rsa-keys.md: fix typo "key-pair nam>>" → "key-pair name>"
- vmware.md: lowercase admonition directive (:::{NOTE} → :::{note})
- vpp/configuration/nat/index.md: remove blank line inside {include} fence

Grammar:
- vpp/configuration/interfaces/loopback.md: "bounded" → "bound"
- vpp/configuration/sflow.md: "VyOS support" → "VyOS supports"
- vpp/requirements.md: "bypass" → "bypasses"
- vpp/configuration/dataplane/interface.md: "configures" → "configure"

CI linter (IP addresses):
- nmp.md: wrap 8.8.8.8 example with stop/start_vyoslinter
- lac-lns.md: wrap LNS config block (contains 8.8.8.8)
- wan-load-balancing.md: wrap whole file (illustrative non-RFC IPs)
- policy/examples.md: replace 192.0.1.1 with RFC 5737 192.0.2.1

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* fix(swap): address Copilot review feedback on swap infrastructure

Category D — drop obsolete canary mechanism settings:
- conf.py: remove '**/md-*.md' from exclude_patterns (no canaries left)
- Makefile: replace malformed '*/_build/*' with '$(BUILDDIR)/**' and drop
  the '*/md-*' ignore (canary files no longer exist)

Category C — script robustness:
- import_myst.py:
  * list_myst_files() now raises SystemExit on git ls-tree failure instead
    of silently returning [] (would have masked typo'd --source refs)
  * list_rst_files() skips _build/ when scanning for .rst stems
  * import_page() rejects stems containing '..' or absolute paths and
    re-checks that the resolved destination stays under docs_dir
  * --dry-run uses a separate "would_import" counter; summary line now
    distinguishes dry-run from actual imports
- swap_sources.py:
  * parse_swap_list() reads with explicit encoding='utf-8'
  * do_restore() validates state file version + entry shape before
    renaming files; raises with actionable message on corruption
  * State file reads/writes use explicit encoding='utf-8' throughout

_swap.txt:
- Wrap long comment line to satisfy 80-character doc-linter limit

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* refactor(swap): rename imported .md files to md- prefix for swap mechanism

Restore the canary file naming convention that swap_sources.py expects:
the imported MyST pages now live as docs/<dir>/md-<name>.md alongside
the existing docs/<dir>/<name>.rst, so swap_sources.py --swap can rename
them into place at build time.

- 254 .md files renamed (every page with a matching .rst counterpart)
- 2 MyST-only pages left at their final names (no .rst exists, no swap
  needed): docs/copyright.md, docs/automation/terraform/terraformvyos.md

All 114 stems listed in docs/_swap.txt now have a corresponding
md-<name>.md source file ready to swap in.

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* docs: address CodeRabbit review feedback on imported MyST pages

Fix issues flagged by CodeRabbit on PR #1857. All issues are pre-existing
in the upstream RST docs and inherited by the MyST conversion.

Real bugs:
- inter-vrf-routing-vrf-lite.md: invalid IPv6 next-hop "2001:db8::*" →
  "2001:db8::1"
- ipsec-pa-route-based.md: vendor mislabel "Cisco" → "Palo Alto"
  (header on line 39 and "Monitoring on Cisco side" section heading)
- bgp-ipv6-unnumbered.md: AS number mismatch between configuration and
  verification output for both routers (Router A: 65020 → 64496;
  Router B: 65021 → 64499)
- qos.md: class 30 used "match ADDRESS20" instead of ADDRESS30 — broke
  the documented pattern (classes 10/20/30 → ADDRESS10/20/30)

Security:
- OpenVPN_with_LDAP.md: redact full PEM private key material from the
  three "set pki ... private key '...'" lines and from the embedded
  OpenVPN client <key> block; replace with <REDACTED> / ...REDACTED...
  placeholders. Public certificates retained.

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* feat(swap): default to serving MyST for all swapped pages

Replace the previously-curated 114-stem _swap.txt with the full set of
254 imported md-prefixed pages, so MD is served by default at build
time. To revert any specific page back to RST, remove its stem from
_swap.txt (or comment it out).

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* fix(ext): handle RST fallback in CmdInclude when _renderer absent

`cmdincludemd` is in `myst_fence_as_directive`, so MyST routes
fence blocks through `render_fence → render_restructuredtext →
MockRSTParser`. In that path `self.state` is a plain docutils Body
with no `_renderer`, crashing the build.

Fall back to `nested_parse` when `_renderer` is unavailable so the
directive works in both MyST and RST/MockRSTParser contexts.

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* feat(conf): copy .md sources into HTML output for plain-text serving

Adds a build-finished hook that mirrors every .md file from the Sphinx
source tree into the HTML output directory verbatim, making unrendered
MyST sources accessible alongside HTML renders at the same URL path.

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* docs: address review feedback from PR #1857

Fix conversion artifacts, typos, grammar errors, and technical
inaccuracies flagged by automated code review (Copilot + CodeRabbit).

Infrastructure: add root-level md-*.md exclusion to conf.py,
fix sphinx-autobuild ignore globs in Makefile.

Content: fix curly quotes, invalid Go panic() calls, shell quoting
in cURL examples, incorrect firewall command paths, typos across
22 documentation files, remove duplicate sections.

🤖 Generated by [robots](https://vyos.io)

---------

Co-authored-by: Claude Sonnet 4.6 <noreply@anthropic.com>

1 files changed, 204 insertions, 0 deletions

diff --git a/docs/contributing/md-debugging.md b/docs/contributing/md-debugging.md
new file mode 100644
index 00000000..d3b4b513
--- /dev/null
+++ b/docs/contributing/md-debugging.md
@@ -0,0 +1,204 @@
+---
+lastproofread: '2025-12-05'
+---
+
+(debugging)=
+
+# Debugging
+
+Two flags are available to help debug configuration scripts. Configuration
+loading issues manifest during boot, so these flags are passed as kernel boot
+parameters.
+
+## ISO image build
+
+If you have trouble compiling your own ISO image or debugging Jenkins issues,
+follow the steps at {ref}`iso_build_issues`.
+
+## System Startup
+
+Debug system startup by examining the configuration file loading from
+`/config/config.boot`. Extend the kernel command-line in the bootloader to
+enable this.
+
+### Kernel
+
+- `vyos-debug` - Add this parameter to the Linux boot line to produce
+  timing results for script execution during commit. If you see an unexpected
+  delay during manual or boot commit, this parameter helps identify bottlenecks.
+  The internal flag is `VYOS_DEBUG`, found in [vyatta-cfg]. Output is directed
+  to `/var/log/vyatta/cfg-stdout.log`.
+- `vyos-config-debug` - During development, coding errors can cause commit
+  failures on boot, potentially preventing CLI initialization. This kernel boot
+  parameter ensures access to the system as user `vyos` and logs a Python
+  stack trace to `/tmp/boot-config-trace`. The file is created only if the
+  configuration load fails.
+
+## Live System
+
+Several flags can be set to change VyOS behavior at runtime. Toggle these flags
+using environment variables or by creating files.
+
+For each feature, create a file called `vyos.feature.debug` to enable it.
+If a parameter is required, place it as the first line inside the file.
+
+Place the file in `/tmp` for one-time debugging (the file is removed on
+reboot) or in `/config` to persist permanently.
+
+For example, `/tmp/vyos.ifconfig.debug` can be created to enable
+interface debugging.
+
+You can also enable debugging using environment variables.
+The environment variable name follows the convention `VYOS_FEATURE_DEBUG`.
+
+For example, `export VYOS_IFCONFIG_DEBUG=""` in your vbash has the same effect
+as `touch /tmp/vyos.ifconfig.debug`.
+
+- `ifconfig` - Display all commands and their responses from the OS on
+  screen for inspection.
+- `command` - Display all commands and their responses from the OS on screen
+  for inspection.
+- `developer` - When a command fails, start a PDB post-mortem session instead
+  of showing a standard error message. This allows developers to debug issues
+  interactively. Because the debugger waits for input, it can prevent the router
+  from booting, so only enable this permanently on production systems if you are
+  ready for potential boot failures.
+- `log` - Send all commands used by VyOS to a log file for inspection. This
+  is useful in rare cases when you need to see what the OS is doing, including
+  during boot. The default file is `/tmp/full-log`, but you can change it.
+
+:::{note}
+To retrieve debug output on the command line, disable `vyos-configd`
+in addition. You can do this one-time with
+`sudo systemctl stop vyos-configd`
+or permanently with `sudo systemctl disable vyos-configd`.
+:::
+
+### FRR
+
+Recent versions use the `vyos.frr` framework. The Python class is located in
+`vyos-1x:python/vyos/frr.py`. It includes an embedded debugger similar to the
+one in `vyos.ifconfig`.
+
+Enable debugging by running: `touch /tmp/vyos.frr.debug`
+
+### Debug Python code with PDB
+
+Sometimes it is useful to debug Python code interactively on the live system
+rather than in an IDE. You can do this using pdb.
+
+Assuming you want to debug a Python script called by an op-mode command, find
+the script by looking up the op-mode definitions, then edit it on the live
+system using vi:
+`vi /usr/libexec/vyos/op_mode/show_xyz.py`
+
+Insert the following statement right before the section where you want to
+investigate a problem (for example, a statement you see in a backtrace):
+`import pdb; pdb.set_trace()`
+
+Optionally, surround this statement with an `if` condition that triggers only
+for the conditions you are interested in.
+
+When you run `show xyz` and your condition triggers, you enter the Python
+debugger:
+
+```none
+> /usr/libexec/vyos/op_mode/show_nat_translations.py(109)process()
+-> rule_type = rule.get('type', '')
+(Pdb)
+```
+
+You can type `help` to get an overview of the available commands, and
+`help command` to get more information on each command.
+
+Common useful commands include:
+
+- examine variables using `pp(var)`
+- continue execution using `cont`
+- get a backtrace using `bt`
+
+### Config Migration Scripts
+
+Starting with VyOS 1.5, a new mechanism is used for config migration that
+improves migration performance. New migrators use only the new format with a
+`migration()` function.
+
+```python
+from vyos.configtree import ConfigTree
+base = ['vpn', 'ipsec']
+def migrate(config: ConfigTree) -> None:
+    if not config.exists(base):
+        # Nothing to do
+        return
+    # do your stuff here
+```
+
+New-style migration scripts can no longer run on their own. However, the new
+migration subsystem handler includes a test kit:
+
+```none
+vyos@vyos:~$ /usr/libexec/vyos/run-config-migration.py --help
+usage: run-config-migration.py [-h] [--test-script TEST_SCRIPT] [--output-file OUTPUT_FILE] [--force] config_file
+
+positional arguments:
+  config_file           configuration file to migrate
+
+options:
+  -h, --help            show this help message and exit
+  --test-script TEST_SCRIPT
+                        test named script
+  --output-file OUTPUT_FILE
+                        write to named output file instead of config file
+  --force               force run of all migration scripts
+```
+
+To test your migration, run:
+
+```none
+vyos@vyos:~$ /usr/libexec/vyos/run-config-migration.py --test-script /opt/vyatta/etc/config-migrate/migrate/quagga/11-to-12 --output-file /tmp/foo /tmp/static-route-basic
+vyos@vyos:~$ cat /tmp/foo
+```
+
+The file `/tmp/foo` contains the migrated configuration.
+
+### Configuration Error on System Boot
+
+Running the latest rolling releases sometimes exposes bugs due to edge cases
+missed in design. File these bugs via [Phabricator](https://vyos.dev/), but you can help narrow
+down the issue by following these steps:
+
+1. Log in to your VyOS system.
+2. Enter configuration mode: `configure`
+3. Reload your boot configuration: `load`
+
+You should see a Python backtrace that helps identify the issue. Attach it to
+the [Phabricator](https://vyos.dev/) task.
+
+### Boot Timing
+
+During the migration and rewrite of functionality from Perl to Python, system
+boot time increased significantly. You can analyze and graph boot time to see
+detailed call sequences during startup.
+
+This uses the `systemd-bootchart` package, which is installed by default on
+VyOS 1.3 (equuleus) and later. Configuration is versioned for comparable
+results. Refer to [bootchart.conf] for the configuration file.
+
+To enable boot time graphing, add the following to the kernel command line:
+`init=/usr/lib/systemd/systemd-bootchart`
+
+You can also make this permanent by editing `/boot/grub/grub.cfg`.
+
+## Priorities
+
+VyOS CLI depends heavily on priorities. Every CLI node has a corresponding
+`node.def` file and possibly an attached script. Nodes can have priorities,
+and on system bootup or any `commit` to the configuration, scripts execute
+from lowest to highest priority. This provides deterministic behavior.
+
+To debug priority issues or see script execution order, use the
+`/opt/vyatta/sbin/priority.pl` script, which lists the execution order of
+scripts.
+
+[bootchart.conf]: https://github.com/vyos/vyos-build/blob/current/data/live-build-config/includes.chroot/etc/systemd/bootchart.conf
+[vyatta-cfg]: https://github.com/vyos/vyatta-cfg