feat(git-tools): consume .mosaic/repo.json declarations in compat mode (T51 WP5b, closes #1413)

Spec of record: docs/plans/2026-08-23_repo-structure-declaration.md
(brain repo) sections 4 (consumption contract), 5.1/5.3/5.4, 1.2a.

New shared lib repo-decl.sh: one consumption surface for the wrappers.
Loads .mosaic/repo.json, classifies absent/invalid/valid via the WP1
validator (5.1: ALL consumers invoke the same script; 5.4 point 1:
invalid = ABSENT + loud error naming file/key/reason), extracts the
consumed fields, normalizes origin for 5.3 comparisons, validates
transitions per 4.2 (a CLI flag is input, not authority), and resolves
host:/ paths FAIL-CLOSED while MOSAIC_HOST_ROOT is unset (1.2a — no
WP5b consumer resolves a path today; the helper exists so the first
that needs one cannot guess). v1 declarations validate but carry no
consumable fields: legacy behavior with a note.

pr-create.sh: base precedence -B (validated as an allowed transition)
-> declared integration_trunk -> legacy WP5a forge-default floor
(unmanaged/absent/v1 per 4.3 reversible class, warn + legacy). Remote
mismatch vs canonical_remote refuses (write path, 5.3).

pr-merge.sh: transition validation per declared flow; the hardcoded
main/next target check survives only for undeclared repos during the
rollout window (4.3 irreversible class, loud warning). Remote mismatch
refuses.

ci-queue-wait.sh: ROUTE CONTEXT only (4.1, C4/jarvis F8/DR2 R9) —
branch-selection semantics untouched, absence silent, invalid reported
per 5.4.

mosaic-worktree.sh: staged rule 4.4 — invalid declaration fails
branch-creation loud, absent warns and proceeds, valid contributes
policy ADVICE only (4.5: placement stays derived; the advisory
worktree_root comparison runs only when MOSAIC_HOST_ROOT is set, per
1.2a warn-and-omit). Consuming via a self-located source line and
set -u-safe env access.

mutate-push-guard.sh: NO change — spec 4.1 names it for push-to-trunk
protection, but the tool as shipped is a mutation-coverage meta-tool
for push-guard.sh with no trunk-protection logic to consult; the
disposition is documented in #1413 rather than force-feeding a fake
consumption.

All wrappers degrade SILENTLY to legacy behavior when repo-decl.sh is
absent from a copied tool subset (a legal deployment shape; a note
there broke single-line diagnostic contracts in
test-pr-merge-message-field).

test-repo-decl-consumption.sh: 67 assertions, green x2, hermetic; runs
RED against pre-change tools via WP5B_TOOLS (49 red there — red-first
evidence). Covers every 5.4 hostile-input class applicable to consumed
fields (missing, malformed, unknown schema_version, v1, unknown key,
bad refs, cross-field, userinfo URL, remote mismatch) plus transition
validation, base precedence, absence policies, staged worktree rule,
route context, and 1.2a fail-closed. Enumerated on the S1 surface
(enumeration guard green: population 71, enumerated 57).

Neighbor suites green: WP5a fallback suite, all six pr-merge suites,
worktree large-repo, help/login/interactive suites. S1 chain failures
(fleet-units systemd bus, invariant_r host Pi version, pr-edit
credential-helper env) reproduce identically at origin/next —
environmental, untouched by this diff. No TS/vitest lane touched
(shell tools only).

packages/mosaic/framework/tools/git/ci-queue-wait.sh

@@ -503,6 +503,28 @@ if [[ -z "$BRANCH" ]]; then
     fi
 fi
 
+# T51 WP5b (spec 4.1, C4/jarvis F8): the declaration adds ROUTE CONTEXT only.
+# Branch-selection semantics are UNCHANGED — the guard keeps inspecting the
+# exact head above. No declaration dependency gates the wait (4.3/DR2 R9:
+# blocking here adds a blocker with no safety gain); absence is silent.
+# shellcheck source=packages/mosaic/framework/tools/git/ci-queue-wait.sh
+if git rev-parse --show-toplevel >/dev/null 2>&1 \
+   && [ -f "$(cd "$(dirname "${BASH_SOURCE[0]}")" && pwd)/repo-decl.sh" ]; then
+    source "$(cd "$(dirname "${BASH_SOURCE[0]}")" && pwd)/repo-decl.sh"
+    repo_decl_load
+    if [[ "$DECL_STATE" == invalid ]]; then
+        repo_decl_report_invalid
+    elif [[ "$DECL_STATE" == valid && "$DECL_SCHEMA" == 2 ]]; then
+        route="feature"
+        if [[ "$BRANCH" == "$DECL_TRUNK" ]]; then
+            route="trunk (integration head)"
+        elif [[ "$BRANCH" == "$DECL_RELEASE" ]]; then
+            route="release branch"
+        fi
+        echo "repo-decl: route context flow=$DECL_FLOW trunk=$DECL_TRUNK release=$DECL_RELEASE; guarded head '$BRANCH' is a $route head (spec 4.1)" >&2
+    fi
+fi
+
 if [[ "$PLATFORM" == "github" ]]; then
     if ! command -v gh >/dev/null 2>&1; then
         record_cannot_assert "github-cli-unavailable"